IDMS Multitasking - when to implement

Products

• IDMS
• IDMS - Database

Issue/Introduction

Sites may want to know how to determine whether a particular IDMS CV is suitable to change to MultiTasking (MT). The consideration is whether there is a report that can be run to indicate whether or not this is a good candidate. 

IDMS is a multithreaded system that supports multiple diverse units of work called tasks. In the past, these tasks shared one operating system subtask. With multitasking support, several IDMS tasks can execute concurrently and each task uses a different predefined operating system subtask.

Environment

Release: All supported releases.

Resolution

IDMS does not have any predictive reports that would show whether or not a CV is a good candidate for MultiTasking,. Most sites considering this feature use the PMARPT02 and DCMT commands to test whether or not MultiTasking is improving response time for users by running them before and after implementing it, and comparing results.
 
The main reason sites implement Multitasking (MT) on IDMS CVs is in an effort to improve response time for applications, by reducing wait time. To implement MT, however, will require slightly more CPU than running a CV without Multitasking. For most sites this increase in CPU is neglible, but it could have an impact if the site is already not getting enough CPU allocations from Z/OS to the CV. Therefore, one thing to review before activation of MT, is to check the effectiveness of MVS CPU allocated by z/OS to the IDMS region. It is useless or even painful to allocate extra TCBs to the IDMS region if z/OS doesn't allocate enough CPU to it. MT uses MPMODE locking which will consume a small amount of extra CPU. If the region is getting ample CPU allocated to IDMS, and if the applications are running too slowly to satisfy end users, then it could be worth it to try implementing MT to see if it helps. After MT activation, watch the TCB's usage with DCMT DIS MPMODE and DCMT DIS SUBTASK EFFECTIVENESS. 

For a general discussion about Multitasking, see Multitasking Support: 
This includes an explanation of how multitasking works, as well as ways to monitor the impact Multitasking is having on a CV. PMARPT02, the Task Summary Report, is a great way to measure changes in overall response time before and after implementing multitasking. This will indicate whether or not the Multitasking has had the desired effect.